共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Zimmermann H. M. Urbassek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(3):423-432
Using molecular-dynamics simulation, we study the processes occurring
after impact of clusters on a rigid wall. Comparing the impact of model
clusters consisting of 13 atoms, or of 13 diatomic molecules with varied
bond strength, the systematics in the results of the collision process
are investigated. Four regimes of impact-induced cluster fragmentation
are identified: intact reflection, shattering into large fragments,
complete fragmentation, and molecule dissociation. The effect of the
number of degrees of freedom activated in the collision on the
translational and internal energies of the reflected fragments is
discussed in detail. As a rule, with increasing number of degrees of
freedom which can be activated in the collision, the translational
energy sinks. On the other hand, for weak intramolecular bonding,
intramolecular vibrations are easily excited at small impact energies,
reducing the resulting translational energy. The presence of even a very
weak attractive well epsilonw at the surface has a major influence
on the sticking behavior of the clusters — and hence also on the
absolute reflected energies — even at impact energies E0 ≫
epsilonw. 相似文献
2.
F.F. Karpeshin J. da Providência C. Providência J. da Providência Jr 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(3):319-326
Two types of extreme collective motion, large-amplitude many-phonon vibration of the ionic core and rotation of the cluster
with high angular momenta, are considered. The interplay between vibration and collective motion towards fission is discussed.
A new mechanism of formation and rupture of the neck is proposed which is based on the Franck-Condon principle, and accounts
for the interplay between vibration and fission. Under rotation, the change of the shape of the cluster and a phase transition
from axially symmetric to triaxial ellipsoid are predicted. For studying the effects, vibrational motion can be induced by
laser radiation. Rotational motion may arise in collisions of clusters.
Received 26 April 2001 and Received in final form 15 October 2001 相似文献
3.
Systematic study of small BN clusters 总被引:2,自引:0,他引:2
S. Guerini P. Piquini 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):17-20
We performed a systematic investigation of the small BxNy (x + y? 6) clusters using the ab initio Hartree-Fock scheme plus second-order perturbation theory. The nature of the potential energy surface extrema are analyzed
through analytical total energy second derivatives. Ionization potentials, binding energies and the stability against some
possible reaction mechanisms are calculated. Based on these results we propose that the growing process for these clusters
is mainly due to the successive incorporation of BN molecules. A discussion of some mass spectrometry experimental results
is also presented.
Received 2 October 2000 相似文献
4.
C. Becker J. Gspann R. Krämer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):301-304
Reactive accelerated cluster erosion (RACE) of single crystal artificial diamond has been used to fabricate various nano-
and microstructures. Carbondioxide clusters of about 1000 molecules are accelerated to 100 keV to act as the eroding agent.
Using movable shadow masks, the accelerated cluster beam may erode staircase structures acting as an optical grating. A cycloid
gear has been generated via a stationary nickel mask. Non-reactive accelerated cluster erosion using argon clusters will be considered for comparison.
Received 30 November 2000 相似文献
5.
G. Chen Z.F. Liu X.G. Gong 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):33-36
We have studied the atomic structure and the electronic properties of Ban clusters by the ab initio molecular dynamics method. We find that a structural transition to the bulk-like structure begins at Ba9 cluster, and the structures of the clusters are transferred to be icosahedral-like around n
= 13. The relatively high stability for Ba4, Ba10 and Ba13 clusters are observed.
Received 1st December 2000 相似文献
6.
M.A. Gaveau M. Briant P.R. Fournier J.M. Mestdagh J.P. Visticot F. Calvo S. Baudrand F. Spiegelman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(2):153-161
Spectroscopic experiments have been performed, providing emission and excitation spectra of calcium atoms trapped on argon
clusters of average size 2 000. The two experimental spectra fall in the vicinity of the calcium resonance line 1P 1 → 1S0 at 422.9 nm. The excitation spectrum consists in two bands located on each side of the resonance line of the free calcium.
In addition, Monte Carlo calculations, coupled to Diatomics-In-Molecule potentials are employed to simulate the absorption
spectrum of a single calcium atom in the environment of a large argon cluster of average size 300. The theoretical absorption
spectrum confirms the existence of two bands, and shows that these bands are characteristic of a calcium atom located at the
surface of the argon cluster and correspond to the excited 4p orbital of calcium either perpendicular or parallel to the cluster surface. The precise comparison between the shape of the
absorption spectrum and that of the fluorescence excitation spectrum shows different intensity ratios. This could suggest
the existence of a non adiabatic energy transfer that quenches partly the fluorescence of trapped calcium. Another explanation,
although less likely, could be a substantial dependence of the calcium oscillator strength according to the alignment of the
calcium excited orbital with respect to the cluster surface. The emission spectrum always shows a band in the red of the resonance
line which is assigned to the emission of calcium remaining trapped on the cluster. When exciting the blue band of the excitation
spectrum, the emission spectrum shows a second, weak, component that is assigned to calcium atoms ejected from the argon clusters,
indicating a competition between ejection and solvation.
Received 7 May 2002 Published online 1st October 2002
RID="a"
ID="a"e-mail: jmm@drecam.saclay.cea.fr
RID="b"
ID="b"URA 2453 du CNRS
RID="c"
ID="c"UMR 5626 du CNRS 相似文献
7.
A. Glotov O. Knospe R. Schmidt E.E.B. Campbell 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):333-336
New experimental data is reported for the absolute cross sections for the fusion reaction channel in single gas-phase collisions
between fullerenes. The experimental data is compared with the results of quantum mechanical and classical molecular dynamics
simulations as well as with simple models. Quantum molecular dynamics simulations are in very good quantitative agreement
with the experimental data. The overall dynamical behaviour can be well-described qualitatively in the framework of simple
models.
Received 2 October 2000 相似文献
8.
V. O. Nesterenko W. Kleinig P. -G. Reinhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):57-64
Recent experimental data on the dipole plasmon in axial sodium clusters Na N + with 11 ≤ N ≤ 57 are analyzed within a self-consistent separable random-phase approximation (SRPA) based on the deformed Konh-Sham functional. Good agreement with the data is achieved. The calculations show that, while in light clusters plasmon properties (gross structure and width) are determined mainly by deformation splitting, in medium clusters with N τ 50 the Landau fragmentation becomes decisive. Moreover, in medium clusters shape isomers come to play with contributions to the plasmon comparable with the ground state one. As a result, commonly used methods of the experimental analysis of cluster deformation become useless and correct treatment of cluster shape requires microscopic calculations. 相似文献
9.
E. Fort F. Pradère A. De Martino H. Vach M. Châtelet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):79-84
We present two complementary techniques that provide detailed diagnostics of supersonic beams involving several species. First,
surface scattering, together with quadrupole mass spectrometer detection, yields the monomer percentage for each species within
the beam. Second, analyses of beam profiles for different masses after scattering by a buffer gas permit determination of
mixed cluster presence and, if any, of cluster sizes and compositions. The two techniques are applied to supersonic expansions
of an argon-nitrogen mixture. We discuss the results that provide new insight in binary nucleation processes.
Received: 6 October 1997 / Revised: 4 November 1997 / Accepted: 13 November 1997 相似文献
10.
E.E.B. Campbell K. Hoffmann I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):345-348
The timescale for the coupling of electronic and vibrational excitation in isolated fullerenes is determined by recording
positive ion time-of-flight mass spectra on excitation with ultrashort laser pulses at 790 nm of the same fluence but different
pulse durations. The coupling leads to the onset of a delayed ionisation “tail” on the parent fullerene ion peak. This occurs
for a pulse duration of 500-1000 fs, depending on laser fluence.
Received 20 October 2000 相似文献
11.
R. Thissen P. Lablanquie R.I. Hall M. Ukai K. Ito 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(3):335-342
Photoionization of rare gas clusters in the innervalence shell region has been investigated using threshold photoelectron
and photoion spectrometers and synchrotron radiation. Two classes of states are found to play an important role: (A) valence
states, correlated to dissociation limits involving an ion with a hole in its innervalence ns shell, (B) Rydberg states correlated to dissociation limits involving an ion with a hole in its outervalence np shell plus an excited neutral atom. In dimers, class A states are “bright”, that is, accessible by photoionization, and serve
as an entrance step to form the class B “dark” states; this character fades as the size of the cluster increases. In the dimer,
the “Mulliken” valence state is found to present a shallow potential well housing a few vibrational levels; it is predissociated by the
class B Rydberg states. During the predissociation a remarkable energy transfer process is observed from the excited ion that
loses its innershell electron to its neutral partner.
Received: 10 February 1998 / Revised: 17 July 1998 / Accepted: 31 July 1998 相似文献
12.
13.
J.U. Andersen C. Gottrup K. Hansen P. Hvelplund M.O. Larsson 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):189-204
Thermionic emission from hot fullerene anions, CN
-, has been measured in an electrostatic storage ring for even N values from 36 to 96. The decay is quenched by radiative cooling and hence the observations give information on the intensity
of thermal radiation from fullerenes. The experiments are analysed by comparison with a simulation which includes the quantisation
of photon energy and the statistics of emission. Experiments with heating of the molecules with a laser beam confirm the interpretation
of the observations in terms of radiative cooling and give an independent estimate of the cooling rate for C60
-. The measured cooling rates agree in general within a factor of two with the prediction from a classical dielectric model
of a thermal radiation intensity of ∼ 300 eV/s for C60 at 1 400 K, scaling approximately with the 6th power of the temperature and with the number of atoms in the molecule.
Received 12 March 2001 and Received in final form 12 June 2001 相似文献
14.
P. Mélinon F. Tournus B. Masenelli A. Perez M. Pellarin J. Lermé M. Broyer B. Champagnon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):337-340
This paper deals with a new type of SiC bonding where silicon atom seems to bridge C60 molecules. We have studied films obtained by deposition of (C60)nSim clusters prepared in a laser vaporization source. Prior deposition, free ionized clusters were studied in a time-of-flight
mass spectrometer. Mixed clusters (C60)nSim were clearly observed. Abundance and photofragmentation mass spectroscopies revealed the relatively high stability of the
(C60)nSi
n
+
, (C60)nSi
n - 1
+
and (C60)nSi
n - 2
+
species. This observation is in favor of the arrangement of these complexes as polymers where the C60 cages may be bridged by a silicon atom. Free neutral clusters are then deposited onto substrate making up a nanogranular
thin film (≃ 100 nm). The film is probed by Auger and X-ray photoemission spectroscopies, but above all by surface enhanced Raman scattering.
The results suggest an unusual chemical bonding between silicon and carbon and the environment of the silicon atom is expected
to be totally different from the sp3 lattice: ten or twelve carbon neighbors might surround silicon atom. The bonding is discussed to the light of the so-called
fullerene polymerization as observed for pure fullerite upon laser irradiation. This opens a new route for bridging C60 molecules together with an appreciable energy bonding, since the usual van der Waals bonding in fullerite could be replaced
by an ionocovalent bond. Such an assumption must be checked in the future by XAS and EXAFS experiments.
Received 15 November 2000 相似文献
15.
R.J. Tarento P. Joyes J. van de Walle 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):355-360
The present study focuses on electronic correlation effects on magnetic energy, the spin-spin correlation function of an octahedron
cluster in the (3↑, 3 ↓) electronic configuration threaded by a magnetic field. Some other spin configurations are also discussed
and various field directions are considered. An accurate diagonalisation technique has been used to solve the Hubbard Hamiltonian.
A result is analysed on a linear energy stabilisation at low magnetic flux. Moreover, two types of antiferromagnetic transition
versus the flux occurring for a correlation term larger than a critical one have been observed, i.e. the likelihood of a charge excitation before the antiferromagnetic transition. Finally, a comparison between the results
obtained from the exact diagonalisation and the Gutzwiller method has been carried out, leading to a suggested modification
of the Gutzwiller approach in order to improve it.
Received 23 June 1999 and Received in final form 28 July 2000 相似文献
16.
E.A. Lord S. Ranganathan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(3):335-343
The packing of tetrahedra in face contact is well-known to be relevant to atomic clustering in many complex alloys. We briefly
review some of the structures that can arise in this way, and introduce methods of dealing with the geometry of the polytope
{3, 3, 5}, which is highly relevant to an understanding of these structures. Finally, we present a method of projection from
S3 to E3 that enables coordinates for the key vertices of the collagen model of Sadoc and Rivier to be calculated.
Received 27 March 2001 相似文献
17.
R. S. Berry 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):5-6
We review some of the ways clusters offer special kinds
of insights both into properties of bulk matter and properties unique to
small systems. We then survey some of the tantalizing open questions that
lie ahead in cluster science. 相似文献
18.
R.-J. Tarento P. Joyes J. van de Walle M. Nakamura 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):111-114
We investigate the electron capture occurring in the collision between an ion A+ and a cluster An (n = 5). The process has been modelled within the Hubbard Hamiltonian,which takes into account the intrasite U electron correlation. An exact procedure has been numerically applied which involves all the excited states to examine the
time evolution of the system during the collision. We have applied the model to the sodium case. We have investigated the
time evolution of the electron population during the collision on the projectile versus the kinetic energy of the projectile. It displays some oscillations which means that the electron exchanges between the ion
and the cluster occurs alternatively in one direction and the other. We also vary U and examine its influence on the dynamics of the oscillation of the average population. Finally the cross section is derived
versus the energy and U.
Received 29 November 2000 相似文献
19.
F. Despa W. Bouwen F. Vanhoutte P. Lievens R.E. Silverans 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(3):403-411
The influence of doping of Li-clusters by electronegative O and C atoms on the ionization potentials was investigated. Experimentally,
we report ionization potentials for bare Lin clusters deduced from photoionization efficiency spectra. The values are compared with the results for LinO and LinC clusters. Observed differences are largely attributed to a quantum size effect caused by the segregated molecular part around
the impurity, which changes the electron work function. Theoretically, the Fermi and exchange-correlation energies which enter
the work function, are calculated in the frame of the augmented plane wave (APW) method by taking explicitly into account
the presence of the molecular core. The other contribution to the work function, the moment of the double layer at the cluster
surface, is computed by solving the corresponding Poisson's equation.
Received 9 September 1999 and Received in final form 7 February 2000 相似文献
20.
Y. Yamaguchi J. Gspann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):103-106
Large-scale molecular dynamics simulations with high acceleration energy on a diamond surface were performed in order to investigate
the surface erosion process. Accelerated argon or CO2 clusters (∼960 atoms, 100 keV/cluster) impacted on the (111) surface of diamond which consisted of more than 1,000,000 carbon
atoms. A typical hemispherical crater appeared about 0.7 ps after the impact, and two or three-layered shockwaves were formed
and propagated to certain directions, but the crater was immediately filled up with the fluidized hot carbon material due
to the collective elastic recovery before the reflection of the shockwave. The impact energy of the cluster was at first transferred
mainly as kinetic energy of the diamond surface in a short time, and the potential energy was activated later. The activated
carbon and oxygen atoms from the impact cluster stimulated the evaporation from the diamond surface for the CO2 cluster impact while the evaporation seemed to be suppressed by the argon atoms themselves for the argon cluster impact.
Received 22 November 2000 相似文献